Manufacture and treatment of cellulose esters



Patented F eb. 20, 1934 UNITED STATES MANUFACTURE AND TREATMENT OFCELLULOSE ESTERS Henry Dreyfus,

London, England No Drawing. Application March 21, 1929, Serial No.348,980, and in 1928 Claims.

This invention relates to the manufacture of cellulose esters of hydroxyaliphatic acids.

The cellulose derivatives are manufactured according to the presentinvention by the treatment I 5. of cellulose or cellulose-containingmaterial with anhydrides of hydroxy aliphatic acids. .For conveniencethe cellulose derivatives thus obtained will be termed hereinafterhydroxyalkacyl derivatives of cellulose. The hydroxy groups thereof '10may be esterified, for instance with acetic anhydride, so as to formacidyloxyalkacyl derivatives of I cellulose.

The acylation with the anhydrides of the hydroxy aliphatic acids may becarried to the mono-, 15 di-, or tri-acyl stage or to any intermediatestage, but the most valuable products are obtained if the reaction withthe cellulose or cellulose-containing material is carried to thetri-acyl stage or to between the diand tri-acyl stage.

The anhydrides tobe used in the acylation may be derived from anyconvenient hydroxy aliphatic acids, for example glycollic acid, lacticacid, hydracrylic acid etc. and may be prepared by any convenientmethod. For example they may be prepared from the sodium, potassium, orother metallic salts of the acids or mixtures thereof by treatment withthionyl chloride.

As initial materials for acylation according to the present inventioncotton or any other celluloses or near conversion products thereof maybe employed, or bamboo, esparto or wood pulps from which the lignin,pentosan, resin and like constituents have been substantially removed,as for example in sulphite pulp, soda pulp and sulphate pulp.

The cellulosic materials may be treated, prior to the acylation, withorganic acids in large or small quantities, and particularly with lowerfatty acids, such as formic or acetic acid, or with 10 hydroxy-aliphatioacids, to increase their reactivity. Chemical pulps are preferablysubjected to an alkaline purifying treatment, as described in my U. S.Patent No. 1,711,110, followed by the treatment with organic acids,prior to the acylation. The alkaline purifying treatment may for examplebe performed with caustic alkali of low concentration, such as 3% orunder, with heating or boiling, or with caustic alkali of highconcentration, such as 540% or more, in the cold or with only slig itheating.

The pretreatment with organic acids may be carried out in any convenientmanner. For example, the cellulosic materials may be pretreated withconcentrated or dilute acids, particularly formic or acetic acid, asdescribed in my French Patent No. 565,654, or, where feasible, with thevapours of the acids, as described in my British Patent No. 263,938, thevapours being employed alone or mixed with air or other inertgas. Afterthe treatment-with organic acids, the cellulosic Great Britain April 18,

materials may be subjected to a stream of air or other inert gas or tosuction or vacuum to remove the organic acids wholly or partially.Formic acid, except when employed in small quantitiea,v

should be substantially removed. If for the pre-' treatment an acid,such as acetic acid, is used which will serve as a solvent diluent inthe subsequent acylation its removal is of course unnecessary. However,in pretreating with organicacids alone I have found that the bestresults are obtained by employing either formic acid, such as 80-10()%formic acid, or a mixture of formic acid with another acid, such asacetic'acid and removing it before acylation.

Another type of pretreatment, which I have found very efficacious forrendering the cellulosic material more reactive, is that described in myBritish Patent No. 312,998. The cellulosic'material is treated withhydrochloric or other hydrohalide acid or with mixtures thereof. Theacid is most advantageously employed in a proportion of 510%(corresponding to about l5-3il% of commercial acid'in the case ofhydrochloric acid).

The aqueous acids may be distributed evenly over the'cellulosicmaterial, for instance by spraying the material in a drum or mixer, thecellulosic material being allowed to stand with occasional turning toensure uniform impregnation until a prodnot capable of rapid acylationis obtained. This type of pretreatment is most valuable when hyment withother mineral acids for example sulphuric acid.

The actual acylation of the cellulose or cellulose-containing materialwith the anhydrides may be carried out in any convenient manner. Forexample it may be conducted in presence of a solvent or mixture ofsolvents for the cellulose derivative produced. Acetic acid or otherlower fatty acids (with the exception of formic acid) may for example beemployed. The invention is however not limited to the use of anyparticular solvent. The solvent or solvent mixture may be present in anydesired quantity such as 4 to 6 times the weight of the cellulose orcelluloseoontaining material, but cellulose derivatives of especiallyhigh viscosity can be obtained if the solvent or solvent mixture bepresent in an hours.

amount greater than 6 times, say 8 to 20 times or more the weight of thecellulose or cellulosecontaining material.

Again the acylation may be conducted in suspension in non-solvent liquiddiluents. If desired solvents may be present in addition to thenon-solvent diluents. As in the acylation carried out in presence of asolvent so that the cellulose derivative is produced in solution, theacetic acid or equivalent solvent may be used in quantities in excess of6 times the weight of the cellulose, for example, 8 to 20 times or moreto obtain cellulose derivatives of high viscosity. In all such cases ofusing solvents in addition in carrying out the acylation in suspension,the diluent should be present in suincient quantity to prevent solutionof the cellulose derivative produced.

Fibres, fabrics or the like made of or containing cotton or othercellulosic material may be acylated by means of the processes of thepresent invention by carrying out the acylation in suspension inpresence of liquid diluents.

The treatment with the anhydrides of the hydroxy aliphatic acids ispreferably conducted in presence of a suitable catalyst or condensingagent. For example, sulphuric acid or organically substituted sulphuricacids such as benzene sulphonic acid, bisulphates, e. g. sodiumbisulphate, phosphoric acid, sulphuryl chloride, zinc chloride or thelike may be employed. Metallic halides, for example the chlorides, ofiron (fer- .ric),.tin (stannic), manganese, copper, nickel or cobalt,used in conjunction with hydrochloric or other hydrohalide acids giveuseful results. Fer- .ric and stannic chlorides may be used withouthydrohalide acid. The quantity of catalyst to be employed will vary withthe catalyst selected and with the type of cellulosic material to betreated.

Sulphuric acid should preferably be employed in proportions under 15%calculated on the weight of the cellulose and especially in proportionsof 1 to 10%, while the ferric chloride, stannic chloride, or otherhalides given above should preferably be employed in a proportion of 5to 20% on the weight of the cellulose, or if used in conjunction withhydrochloric or other hydrohalide acid both the halide itself and thehydrohalide acid should preferably be present in proportionsof between 5and 15% on the weight of the cellulose.

In order to avoid degradation of the cellulose molecule the acylation isconducted at as low a temperature as possible. Temperatures notsubstantially exceeding 50 0., for example 20-30 C., atmospherictemperatures, or temperatures below atmospheric, e. g. 0-l0 C., arepreferable. Ferric chloride .or other of the halide catalysts givenabove do however permit of the acylation being conducted with moderateheating without subsantially impairing the qualities of the productsobtained.

The following examples illustrate the invention but are not to beconsidered as limiting it in any way Example 1 100 parts by weight ofcotton cellulose are pretreated with formic acid, for example bytreatment with 500-1000 parts of formic acidof about 85% strength,allowing to stand for some hours in the cold and hydro-extracting or byimpregnating with about 15 parts of formic acid of '75.85% strength andallowing to stand for 8-12 The material is then washed, centrifuged anddried. The pretreated cellulose is then introduced into a mixture of 600parts of acetic acid, 500 parts of glycollic anhydride and 10 to 12parts of sulphuric acid. If necessary slight heating may be applied toinitiate the reaction but throughout the acylation the temperatureshould not be allowed to rise much above 50 C. When solution iscomplete, the cellulose glycollatemay be separated from its solution byaddition of a non-solvent, for example by addition of excess ofwater. Itis soluble in diluted chloroform-alcohol and in aqueous acetone.

Example 2 100 parts by weight of cotton cellulose are pretreated as inExample 1 and are then introduced into a mixture of 500 parts of aceticacid, 400 parts of glycollic anhydride and 25 to 30 parts of sulphurylchloride. Here again initial heating may be necessary. The temperatureof the mixture is maintained at fill- C. until solution is complete.

Example 3 100 parts by weight of cotton cellulose are impregnated with amixture of 20 parts of ferric chloride and 20 parts of 35% aqueoushydrochloric acid and allowed to stand in the cold for as hours. Thecellulose is then-introduced into a mixture of 600 parts of acetic acidand 450parts or" glycollic anhydride. The acylation is effected at 4050C. until solution is complete, when water may be added to destroy theremaining anhydride.

While the invention has been described above more particularly withreference to the produc tion of cellulose derivatives of glycollic acid,it is also applicable to the production of derivatives of higherhydroxy-aliphatic acids. Furthermore mixed derivatives may be producedby employing another anhydride, e. g. anhydrides of acetic acid and itshomologues, in addition to the hydroxyaliphatic anhydrides. The mixedderivatives may, for example, be produced by treating first with ahydroxy-aliphatic acid anhydride and then with a fatty acid anhydride.

As stated above the hydroxyalkacyl derivatives or mixedalkacyl-hydroxyalkacyl derivatives of cellulose produced according tothe present invention may be treated with esterifying agents, forexample acetic anhydride, to produce derivatives in which the hydroxygroups have been wholly or partially converted into ester groups. Suchderivatives may be termed acidyloxyalkacyl derivatives or mixedalkacyl-acidyloxyalkacyl derivatives of cellulose. For example thecellulose derivative of acetylglycollic acid may be obtained by treatingthe glycollic derivative of cellulose with acetic anhydride. If intreating a lower cellulose glycollate with acetic anhydride, as referredto above, the anhydride be employed in sufficient quantity, a mixedcellulose acetateacetylglycollate results directly.

Example 4 100 parts of cotton cellulose pretreated as inacetylglycollate is very similar in solubility and other properties tocellulose acetate.

I have further found that the cellulose derivatives made according tothe present invention whether they be hydroxyalkacyl or acidyloxyalkacylderivatives or the mixed derivatives containing in addition alkacylgroups may be subjected to secondary treatments or reactions for thepurpose of changing their solubilities. The secondary treatments orreactions may, for example, be carried out in presence of inorganic ororganic acids or acid salts, the treatment being arrested when therequired solubility has been reached. In carrying out the secondarytreatments in the primary acylation solutions or suspensions, theacylation catalysts themselves are in most cases sufficient to effectany desired change in solubility properties.

Example The primary acylation solution of Example 1 (i. e. the solutionobtained before any separation of cellulose glycollate) is treated with-80 parts of water at a temperature of about 35 C. The celluloseglycollate becomes progressively soluble in organic solvents, e. g.acetone, containing more and more water. The treatment is stopped whenthe required solubility has been reached.

While the secondary or further treatments of the primary products maywith advantage be conducted at ordinary or moderate temperatures, thereaction may, if desired, be quickened by heating up to relatively highor high temperatures, even up to or 100 C. but in such cases thepresence of free mineral acids is preferably avoided.

What I claim and desire to secure by Letters Patent is:-

1. Process for the production of' cellulose esters containinghydroxyalkacyl groups, comprising treating materials consistingessentially of cellulose with hydroxyaliphatic acid anhydrides.

2. Process for the productionof cellulose esters containinghydroxyalkacyl groups, comprising treating materials consistingessentially of cellulose with hydroxyaliphatic acid anhydrides inpresence of acylation catalysts.

, 3. Process for the productionof cellulose esters containinghydroxyalkacyl groups, comprising treating materials consistingessentially of cellulose with hydroxyaliphatic acid anhydrides inpresence of sulphuric acid.

4. Process for the production of cellulose esters containing glycollylgroups, comprising treating materials consisting essentially of.cellulose with glycollic anhydride in presence of acylation catalysts.

5. Process for the production of cellulose esters containing glycollylgroups, comprising treating materials consisting essentially ofcellulose with glycollic anhydride in-presence of sulphuric acid.

6. Process for the production of cellulose esters containing glycollylgroups, comprising treating materials consisting essentially ofcellulose with glycollic anhydride in presence of acylation catalystsand a liquid acylation medium.

7. Process for the production of cellulose esters containing glycollylgroups, comprising treating materials consisting essentially ofcellulose with organic acids and then with glycollic anhydride inpresence of acylation catalysts.

8. Process for the production of cellulose esters containing glycollylgroups, comprising treating materials consisting essentially ofcellulose with organic acids and then with glycollic anhydride inpresence of acylation catalysts and a liquid of acylation catalysts anda liquid acylation medium.

10. A cellulose ester in which part of the cellulose nuclear'hydroxylgroups are esterified by alkacyl groups and part by hydroxy-alkacylgroups.

11. A cellulose acetate-glycollate in which part of the cellulosenuclear hydroxyl groups are esterified by acetyl groups and part byglycollyl groups.

12. Process for the manufacture of cellulose esters containinghydroxyalkacyl groups, comprising treating materials consistingessentially of cellulose with hydroxy aliphatic acid anhydrides andsubjecting the resulting primary hydroxyalkacyl esters to the action ofacidic substances for the purpose of changing their solubilitycharacteristics.

13. Process for the manufacture of mixed cellulose esters containinghydroxyalkacyl and alkacyl groups, comprising treating materialsconsisting essentially of cellulose separately with an hydroxy aliphaticacid anhydride and a simple aliphatic acid anhydride both in thepresence of acylation catalysts and a liquid acylation medium. andsubjecting the resulting mixed primary cellulose esters to the action ofacidic substances for the purpose of changing their solubilitycharacteristics.

14. Process for the manufacture of cellulose esters containinghydroxyalkacyl groups, comprising treating materialsconsistingessentially of cellulose with hydroxy aliphatic acid anhydrides andsubjecting the resulting primary hydroxyalkacyl esters to the action ofthe substances having mineral acidity for the purpose of changing theirsolubility characteristics.

15. Process for the manufacture of cellulose glycollates comprisingtreating materials consisting essentially of cellulose with glycollicanhydride and subjecting the resulting primary.

cellulose glycollates to the action of acidic substances for the purposeof changing theirsolubility characteristics.

16. Process for the manufacture of mixed cellulose esters containingglycollyl and acetyl groups, comprising treating materials consistingessentially of cellulose separately with glycollic anhydride and aceticanhydride both in the presence of acylation catalysts and a liquidacylation medium, and subjecting the resulting mixed primary celluloseesters to the action of acidic substances for the purpose of changingtheir solubility characteristics.

17. Partially hydrolyzed hydroxyallsacyl esters of cellulose.

18. Partially hydrolyzed cellulose glycollates.

l9. Partially hydrolyzed mixed cellulose esters in which part of thenuclear hydroxyl groups are esterified by alkacyl groups and part byhydroxyalkacyl groups. v

20. Partially hydrolyzed mixed cellulose esters in which part of thenuclear hydroxyl groups are esterified by acetyl groups and part byglycollyl groups.

HENRY DREYFUS.

